marcelosb

Behavior of variables read by Prosoft MVI56-MNETR in case of network failure

4 posts in this topic

Hello!

I have one Controlllogix project that communicates with a modbus slave through modbus TCP, using a Prosoft module model MVI56-MNETR.

Does anyone know what happens to the data polled in case the network fails? Do all variables go to zero or do they freeze in their last value (or something else entirely)? I couldn't find anything in the Prosoft manual.

Thanks for any help!

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I read the manual and also came up with nothing, so I can only make an educated guess based on experience with other similar networks & comm cards. Also, I should mention it's been quite a while since I've worked with anything below Studio5000 V21.

I'm assuming the modbus data from other network devices (ie other controllers, drives, sensors, etc) is being moved to/from those devices and tags within the controller that owns the Prosoft card. If the network fails for any reason, I'm guessing that it would be similar to any other Ethernet failure; the field devices maintain their respective values except for ongoing responses to the process, the tags within the controllers (usually) retain their values according to the last program scan, and any data that was actively in "transit" is lost. 

In addition, I read in the user manual that this Prosoft card requires an unconditional AOI be installed in the project of the controller that owns it. In every communication instruction I've worked with, when that instruction is interrupted (controller is put in program mode, network fails, etc) the data being transferred is lost. In other words, there is never a partial transfer of data from a MSG instruction, produced/consumed tag, etc. I'm guessing it's is the same for this instruction/comm card, but truly can't say that with any certainty. 

I think you may be able to test this by creating a few "dummy" tags in the controller, and then hooking up a few "dummy" devices to any spare places on the Modbus. Verify the data is getting to the controller, then disconnect the comm cables from the Prosoft card and observe the tag values. 

If you can't test this, you might consider writing a fault routine to handle a network failure worst case scenario. If you can test this or find a definitive answer, please let me know!

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@ElectronGuru thank you so much for the info!

I would also bet that the data freezes. I will propose a short program to check for communication failure in order to take the appropriate response.

If I manage to test the situation I will come back here and report.

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@ElectronGuru

We tested the communication failure by removing the ethernet cable. The variables really do freeze.

So now we know for sure!

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